1898.] on Luing Crystals, 731 



place, it is very evident that these adaptations did not come into 

 existence suddenly, like an instantaneous pliotograph as it were, but 

 are the result of a long and gradual course of evolution from the 

 simple crystal, formed, so to speak, almost by chance in the molecular 

 ferment and turmoil that goes on in the living organism, up to the 

 highly perfected and elaborated forms of spicules which compose 

 the supporting framework in different species of sponges. In the 

 second place, the persistence of different species of sponges in certain 

 grades of evolution shows that the adaptation in any given case is 

 not to be regarded as perfect, but only as slightly better or worse 

 than that seen in other species. This points to the main factor in 

 the evolution having been the natural selection consequent upon 

 competition and the struggle for existence. 



[E. A. M.] 



